The proposed study will assess the effect of local heat therapy on jaw pain and jaw fatigue secondary to a teeth clenching task in chronic TMD pain cases. Researchers expect that most participants will respond to heat therapy and consequently experience reduced jaw pain and fatigue during teeth clenching. The study will assess the clinical characteristics of those participants who respond and do not respond to local heat therapy, in order to determine the common clinical characteristics for those in each response category.

Inclusion Criteria:

• Provide signed and dated informed consent form.

• Willing to comply with all study procedures and be available for the duration of study participation.

• Be 18 years or older.

• Have a minimum set of teeth present, be it natural, implant-supported or fixed prosthodontics: all anterior teeth (incisors, canines), at least one premolar, at least one molar (first or second molar; third molars not considered).

• TMD-Pain screener score equal to or greater than 3

• Myalgia (masticatory muscle pain) based on clinical exam following the DC/TMD protocol

• Concurrent arthralgia (TMJ pain) and/or headache attributed to TMD allowed

• Myofascial pain must meet the following criteria:

  1. Onset >3 months, occurring >15 days/month on average in the last three months from the screening session
  2. Minimum of 10 jaw pain episodes since onset, each episode lasting at least 30 minutes and no less than 2 hours within the day, OR unremitting

Exclusion Criteria:

• Traumatic facial injury or surgery on the face/jaw, arms or hands;

• Presence of pain related to dental and periodontal pathology;

• Currently undergoing active orthodontic treatment;

• Pregnant;

• Has any of the following medical conditions by self-report:

  1. Renal failure or dialysis,
  2. Heart disease (examples: uncontrolled arrythmia or hypertension, cardiomyopathy) or heart failure, Non-allergic bronchospasm (chronic obstructive pulmonary disease and emphysema),
  3. Diabetes (type I or II) that is not controlled with medication or diet,
  4. Hyperthyroidism,
  5. Uncontrolled seizures;

• Used any injection therapy (e.g., tender or trigger point injections, steroid injections), acupuncture, biofeedback, or TENS for the management of facial/jaw pain within 2 weeks prior to the screening assessment; If undergoing botulinum toxin injections in the head and neck area, must be 3 months since last set of injections and refrain from this treatment until study participation has ended

• History of major depression or other major psychiatric disorder requiring hospitalization within the last 6 months prior to the screening assessment;

• History of treatment for drug or alcohol abuse within the last 12 months;

• Current pain medication use (e.g., opioids, ibuprofen, acetaminophen) that cannot be stopped <24 hours prior to each study visit;

• Current use of medically prescribed muscle relaxants for the duration of study participation;

• Other conditions/diseases associated with altered pain perception: neurological or development disorders (dementia, autism spectrum disorder), neoplasm, multiple sclerosis, trigeminal neuralgia;

• Adults lacking capacity to provide informed consent for themselves;

• Unable to understand instructions for study procedures in English.

• Anything that would place the individual at increased risk or preclude the individual's full compliance with study procedures or completion of the study."